The work aims to improve adsorption property of activated carbon for CO2. Phase of activated carbon before and after surface treatment was analyzed with X-ray diffractometer in DETA impregnation method. Specific surface area and pore structure of the activated carbon before and after surface treatment were analyzed with full-automatic specific surface & voidage analyzer. Finally, an adsorption experiment and theoretical analysis were performed to the activated carbon before and after surface treatment. Carbon in the activated carbon subject to surface treatment changed from trigonal system to hexagonal system. And amino group was added on the surface of activated carbon. Specific surface area of the activated carbon increased by 2.13 times; microporosity increased by 1.80 times, from 0.056 cm3/g to 0.157 cm3/g; total porosity increased by 3.24 times, from 0.078 cm3/g to 0.331 cm3/g; increment of midporosity was 0.152 cm3/g; mean pore size decreased by 0.27 nm, from 7.14 nm to 6.87 nm. Adsorption capacity of the activated carbon increased from 0.92 mmol/g to 3.55 mmol/g, which was 3.86 times as high as that before surface treatment. Saturated adsorption time increased from 10 min to 40 min. This method can effectively improve the adsorption property of activated carbon.